The present invention relates to a sizing sleeve arrangement for controlling the outer diameter of a plastics tube being produced by a continuous tube forming process such as extrusion, or by an expansion process such as that generally described in International Patent Application No. WO 90/02644, wherein the tube at least in the region of the sizing sleeve is under positive internal pressure. The invention also relates to a method of controlling the diameter using the sizing sleeve.
It is known to provide sizing sleeves for tube diameter control with passages allowing the injection of lubricating water between the sleeve and the travelling tube, for example as achieved by a helical channel about the sleeve as described in PCT/FI90/00214 and EP 0 385 285 A2. In the case where the inside of the tube is not pressurized, these sizing sleeves may also have apertures in the sizing sleeve for applying a vacuum to the outside of the tube.